Method of manufacturing a printing substrate

ABSTRACT

An optical scanning system and method for laser engraving a plurality of data subrasters into a substrate to form a raster of engraved data defining an image on the substrate. Each subraster has a length dimension and a width dimension. The system includes a transport assembly having an objective lens and a mirror, the mirror capable of reflecting a substantially collimated scanning beam incident thereon in a direction transverse to an axis of the incident beam such that it is directed to the objective lens. The objective lens is capable of focusing the scanning beam on the substrate to engrave a set of data in the width dimension of the subraster and the objective lens and mirror combination is capable of moving along the axis of the incident beam to allow subsequent engraving of other sets of data in the width dimension until a complete subraster is formed along its length dimension. The objective lens and mirror combination is also capable of returning to its starting position to begin engraving of a subsequent subraster of the plurality of subrasters forming the raster of engraved data. A thermoset plastic substrate and a substrate having a an inorganic ceramic material are also identified as being suitable for use in a printing process, and particularly suitable for use with the aforementioned system and method.

RELATED APPLICATIONS

[0001] This application is a continuation-in-part of U.S. patentapplication Ser. No. 10/159,492, filed May 31, 2002, upon which a claimof priority is based.

TECHNICAL FIELD

[0002] This invention relates to direct laser engraving of a flatsubstrate for use in a printing process, such as intaglio printing. Moreparticularly, the invention relates to an optical scanning system andsubstrate material particularly suitable for high-speed andhigh-resolution engraving.

BACKGROUND OF THE INVENTION

[0003] Many printing processes utilize substrates, platens or forms asprinting surfaces to transfer an image to a printable medium. One suchprocess is called intaglio printing. Intaglio printing involvesapplication of printed indicia or images below the surface of a platenor substrate that is utilized as a printing surface. Traditionally,intaglio substrates have been prepared by mechanically engraving orchemically etching a recessed pattern into the printing surface of thesubstrate, which defines an image. The pattern may comprise an array ofdots in the printing surface of the substrate. The recessed pattern,such as the array of dots, define tiny recesses within which ink is heldand transferred to the printable medium, such as a sheet or surface.This intaglio process is typically used in die stamping or in engravedprocesses, sometimes referred to as copper plate printing. It is alsoused in connection with pad printing, which is typically used todecorate plastic surfaces, as well as in the gravure printing process.

[0004] Mechanical engraving and chemical etching techniques aretime-consuming processes. Mechanical techniques are typically slow dueto limitations of engraving equipment. A mechanical stylus must be usedto engrave the image into the substrate, which requires a certain amountof time to penetrate and cut the substrate material. Furthermore,accuracy of the engraving becomes an issue when the stylus becomes wornand dull. On the other hand, chemical etching is time consuming due tothe many steps involved. Chemical etching is a multi-step process thatfirst involves producing the image onto a film negative, such as with animagesetter. Once the film is produced, it becomes a mask that can belaid on top of a copper or steel substrate having a thin film coating ofsensitizing material. The substrate and mask combination is exposed tolight for subsequent chemical development, which transfers the mask tothe copper plate. After development, the substrate is ready for acidetching to complete the process. Accuracy is also an issue with chemicaletching, due to the limited controllability of the chemical-etchingprocess.

[0005] Another technique involves direct laser etching, which is asingle-step process that requires much less time than mechanicalengraving and chemical etching techniques. In this technique, a laser isused to directly engrave the substrate material. However, because metalshave a high reflectance, the laser/metal interaction is not conducive toproducing plates having sharp engravings. With metals and a majority ofplastics, direct laser engraving causes the material to melt, whichcreates the recessed areas, but also creates pooling of melted materialaround these recessed areas. This pooling of material acts as a ridgesurrounding the recessed areas, which adversely affects the accuracy andusefulness of the printing surface of the substrate. Thus, accuracyremains an issue. Furthermore, although the direct laser technique isonly a single-step process, the speed of the engraving process stillremains an issue at higher resolution levels, which require the laser toengrave a higher number of tightly focused dots to achieve suchresolutions. With presently known systems, the engraving process time isincreased when the resolution level is increased.

[0006] The system and method of the present invention addresses theseand other problems associated with direct laser engraving of substrates.

SUMMARY OF THE INVENTION

[0007] An optical scanning system for laser engraving a plurality ofdata subrasters into a substrate to form a raster of engraved datadefining an image on the substrate. Each subraster has a lengthdimension and a width dimension. The system includes a transportassembly having an objective lens and a mirror, the mirror capable ofreflecting a substantially collimated scanning beam incident thereon ina direction transverse to an axis of the incident beam such that it isdirected to the objective lens. The objective lens is capable offocusing the scanning beam on the substrate to engrave a set of data inthe width dimension of the subraster and the objective lens and mirrorcombination is capable of moving along the axis of the incident beam toallow subsequent engraving of other sets of data in the width dimensionuntil a complete subraster is formed along its length dimension. Theobjective lens and mirror combination is also capable of returning toits starting position to begin engraving of a subsequent subraster ofthe plurality of subrasters forming the raster of engraved data.

[0008] In a particular embodiment, an optical scanning system for laserengraving of a plurality of subrasters of data into a substrate to forma raster of engraved data is provided and includes a scanner capable ofdeflecting an input laser beam incident thereon from a first beamdirection to create a scanning beam. The system also includes a beamexpander capable of receiving the scanning beam and expanding it tocreate an expanded scanning beam. A transport assembly of the system hasan objective lens and a mirror, wherein the mirror is capable ofreflecting the expanded scanning beam in a second beam directiontransverse to the first beam direction such that it is incident on theobjective lens. The objective lens and mirror is capable of moving alongan axis defined by the first beam direction. The objective lens iscapable of focusing the expanded scanning beam on the substrate toengrave a set of data oriented in a width dimension of the subraster andis also capable of moving along the first beam axis to allow subsequentengraving of other sets of data oriented in the width dimension until acomplete subraster is formed to define a length dimension of thesubraster. The objective lens and mirror combination is further capableof returning to its starting position to initiate engraving of asubsequent subraster.

[0009] According to another aspect of the invention, an optical scanningsystem is provided that is capable of engraving at two differentresolutions.

[0010] According to another aspect of the invention, a substrate isprovided for use with a direct laser engraving process to create anintaglio printing substrate. The substrate consists essentially of athermoset plastic which substantially vaporizes in response to animpinging laser beam that engraves portions of the substrate, therebysubstantially eliminating the formation of slag material adjacent toengraved portions of the substrate.

[0011] According to another aspect of the invention, a substrate isprovided for use with a direct laser engraving process to create aprinting substrate, wherein the substrate comprises a base material andan inorganic ceramic material disposed on the base material.

[0012] According to yet another aspect of the invention, methods ofmanufacturing such a substrate and methods for making such a substrateinto a printing substrate in accordance with the principles of thepresent invention are provided.

[0013] According to yet another aspect of the invention, a method oflaser engraving a substrate for use in a printing process is provided.The method comprises the steps of: (a) directing a substantiallycollimated scanning beam having a beam axis to an objective lens that ismovable along the beam axis, wherein the scanning beam defines a scanwidth; (b) focusing the scanning beam through the objective lens andonto the substrate; (c) engraving onto the substrate a set of subrasterwidth data having a width equal to the scan width of the beam; (d)continuously moving the objective lens along the beam axis to subsequentpositions relative to the substrate and engraving subsequent sets ofsubraster width data to form a complete subraster; (e) incrementing thesubstrate and engraving an additional subraster adjacent to thepreviously completed subraster; and (f) repeating the steps ofincrementing the substrate and engraving an additional subraster until acomplete raster made up of a plurality of subrasters is created thatdefines an engraved image on the substrate.

[0014] These and other aspects of the invention will become apparentfrom the specification, drawings and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

[0015]FIG. 1 is a schematic diagram of an embodiment of a direct laserengraving system in accordance with the present invention.

[0016]FIG. 2 is a top plan view of a portion of the system of FIG. 1.

[0017]FIG. 3 is a side elevational view of the portion of the systemshown in FIG. 2

[0018]FIG. 4 is a detailed top plan view of the scanner and first lensof the beam expander shown in FIG. 2.

[0019]FIG. 5 is a schematic diagram of a byte and bit layout of asampling of data sets of a subraster in a sample 1200 dpi scan inaccordance with the principles of the present invention.

[0020]FIG. 6 is a functional block diagram of data handling of thesystem of FIG. 1.

[0021]FIG. 7 is a schematic diagram of an embodiment of a substrate inaccordance with a particular aspect of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0022] While this invention is susceptible of embodiments in manydifferent forms, there is shown in the drawings and will herein bedescribed in detail one or more preferred embodiments of the inventionwith the understanding that the present disclosure is to be consideredas an exemplification of the principles of the invention and is notintended to limit the broad aspect of the invention to the embodimentsillustrated.

[0023]FIG. 1 depicts a schematic diagram of an embodiment of an opticalscanning system 10 in accordance with the principles of the presentinvention. The system 10 can be utilized for laser engraving a substratefor use in a printing process. A particular feature of the system 10 isthe ability to engrave at two different resolutions with the sameoptical system. In a preferred embodiment, the system 10 is capable ofengraving at 1200 dpi and 2400 dpi. Referring to FIG. 1, the system 10includes a polygon scanner 20, a beam expander 22 and a transport (ortrolley) assembly 24. A receptor assembly 26 is disposed adjacent to thetransport assembly 24 and supports the substrate to be engraved. Thereceptor assembly 26 is capable of incrementally translating thesubstrate with respect to the transport assembly 24 via a steppedtransport. As will be discussed in more detail below, the transportassembly 24 includes a mirror 27 and an objective lens 28 that are alsomovable to facilitate the engraving process.

[0024] The system 10 requires an input beam 30. A laser assembly 31 isprovided to produce the input beam 30, which is incident on the scanner20 from a first beam direction. The laser assembly 31 includes a laser32 (preferably a DC excited CO₂ laser), a beam compressor 34 and amodulator 36 driven by a modulator driver 38. Referring to FIG. 1, thelaser 32 produces a beam 40 (having a beam width A) that is shaped bythe beam compressor 34 to produce a compressed beam 41 (having a beamwidth B). The compressed beam 41 is modulated by the modulator 36 toproduce the input beam 30 (having a beam width C). Preferably, the beamwidth A of the beam 40 is 8mm, the beam width B of the compressed beam41 is 1 mm, and the beam width C of the input beam is 1 mm. The inputbeam 30 is scanned by the scanner 20 to produce a scanning beam 42,which is directed to the beam expander 22. As will be explained in moredetail below, the beam expander 22 produces a substantially collimatedexpanded scanning beam 50 (having a beam width D), which is directed tothe mirror 27 and objective lens 28 combination of the transportassembly 24. The mirror 27 reflects the beam 50 to the objective lens28, which focuses the beam onto the substrate. Preferably, the beamwidth D of the expanded scanning beam 50 is 20 mm and the mirror 27 isangled at 45 degrees. Essentially, the beam expander 22 expands thescanning beam 42 and relays it to create the expanded scanning beam 50,which has a substantially constant width over an extended distance.

[0025]FIGS. 2 and 3 depict the system 10 in more detail. FIG. 2 is a topplan view of the system 10 and FIG. 3 is a side view of FIG. 2. In apreferred embodiment, the scanner 20 is a polygon scanner having 15facets and is rotatable in a direction indicated by rotational arrows inFIGS. 2 and 3. In a preferred embodiment, the scanner rotates at either10,000 rpm or 20,000 rpm, depending on desired resolution. Consideringthe scanner 20 as a nutating mirror executing ±10° mechanical deflectionof the input beam 30, the input beam 30 is deflected ±20° due to mirrordoubling to produce the scanning beam 42. As shown in FIGS. 2 and 3, thebeam expander 22 includes a first lens L1 and a second lens L2.Referring to the detailed view of the scanner 20 and the first lens L1of the beam expander 22 in FIG. 4, the scanning beam 42, which is asubstantially collimated beam having a beam width C and deflected ±20°,is directed to be incident on lens L1. In a preferred embodiment, lensL1 has a focal length of 15 mm. The lens L1 is located one focal lengthf1 from the scanner surface and acts telecentrically such that the ±20°beams continue to the right of the lens L1 and remain substantiallyparallel to a lens axis 60, while deflected components of the beamsconverge to a focal plane 64 one focal length f1 beyond the lens L1.Referring to FIG. 2, beyond the focal plane 64, an upper limit beam 66and a lower limit beam 68 of the deflected beam components expand.Referring to FIG. 3, the focal plane 64 acts as a plane of beamsymmetry, as shown in FIG. 3.

[0026] The upper limit beam 66 and the lower limit beam 68 expand untilthey reach a second lens L2, which is spaced a focal length f2 from thefocal plane 64 of the first lens L1. In a preferred embodiment, thefocal length f2 is 300 mm. Utilizing the preferred pair of lenses L1 (15mm focal length) and L2 (300 mm focal length), the beam expander 22 actsas a 20× beam expander (300/15=20). Thus, the beam expander 22 in thepreferred embodiment expands the 1mm input beam to a substantiallycollimated 20mm output beam. A fundamental consequence of beam expansionis a complimentary compression of scan angle of the beam (in thepreferred embodiment, compression from ±20° to ±1°). This reduction inscan angle imparts a practical field angle to the objective lens 28.

[0027] Another consequence of this configuration in the preferredembodiment is the relaying of a 1mm beam aperture at the scanner 20 to a20 mm beam aperture at the 300 mm focal distance of lens L2. Thus, asshown in FIG. 2, although the beams shift laterally (due to deflection)in the long region between the scanner 20 and the objective lens 28, thebeam shift reduces to zero at a distance E beyond lens L2 (300 mm in apreferred embodiment). In other words, the stability of the 1 mm beam atthe scanner 20 (scanning beam 42) is transferred as a stable 20 mm beam(expanded scanning beam 50) at the objective lens 28. As explained inmore detail below, in a preferred embodiment, the 300 mm distance is anominal beam travel length for the objective lens 28 with respect to itsmovement on the transport assembly 24 along a beam axis 70 of theexpanded scanning beam 50.

[0028] Referring again to FIGS. 2 and 3, the transport assembly 24facilitates movement of the mirror 27 and the objective lens 28 alongthe beam axis 70 of the expanded beam 50. The mirror 27 and theobjective lens 28 combination are movable within the transport assembly24 in both directions for a distance F along the beam axis from thenominal position, for a total travel of 2F. In a preferred embodiment,the transport assembly 24 facilitates movement of the mirror 27 and theobjective lens 28 for 4 inches (F=4 inches) in each direction for atotal range of travel of 8 inches (2F), which corresponds to a dimensionof an image format size, which is 8″×10″ in a preferred embodiment. Ofcourse, other format sizes could be accommodated through adjustment ofthe system in accordance with the principles of the present invention.

[0029] Referring to FIG. 3, the expanded scanning beam 50 is interceptedby the mirror 27 and reflected, thereby folding the beam 50 so that itis incident on a principal plane 80 of the objective lens 28. The beam50 is intercepted by the mirror 27 at a nominal position of G, foldingthe remaining length (E-G) to complete the nominal distance E (300 mm ina preferred embodiment) to the principal plane 80 of the objective lens28. At the objective lens 28, the beam width of beam 50 (20 mm in apreferred embodiment) is converged over a focal distance (f3) of thelens 28 to an energetic focal point to engrave the surface of thesubstrate material. The transport assembly 24 transports the mirror 27and the objective lens 28 over a dimension of the format size (2F). Forsimplicity of illustration, the limit positions of the mirror 27 and theobjective lens 28 are represented in FIG. 3 by the two mirrors shown inphantom lines. It is understood that the mirror 27 and the objectivelens 28 move in combination.

[0030] Referring to the right side of FIG. 2, it is noteworthy that witha collimated beam incident on the objective lens 28, even though thebeam position in the aperture of the lens 28 shifts slightly duringtransport, the fundamental criterion for accurate placement of theengraving focal point, which is the angle of the collimated beam withrespect to the lens axis, remains a constant of the system. As explainedbelow, this establishes uniformity of a width dimension of each of aplurality of subrasters of data engraved to form, in combination, anengraved image.

[0031] The present invention utilizes a method of engraving thesubstrate wherein a plurality of data subrasters are engraved to formindividual swaths, which, in combination form a complete raster of datarepresenting an image to be engraved. Referring to the schematic diagramof FIG. 5, a byte and bit layout of a sampling of data sets 102 of asubraster in a sample 1200 dpi scan is shown in accordance with theprinciples of the present invention. Each data bit of the data sets 102represents a point, or dot, of the image to be engraved. As shown inFIG. 5, each subraster 104 comprises a plurality of data sets in a widthdimension of the subraster. In the 1200 dpi resolution example, eachdata set 102 comprises 40 dots across the width dimension of thesubraster (5 sets of 8 dots). In a 2400 dpi example (not shown), eachdata set comprises 80 dots across the width dimension of the subraster(10 sets of 8 dots). The expanded scanning beam 50 engraves each dataset across the subraster width as the transport assembly 24 moves themirror 27 and objective lens 28 combination in a direction along thelength dimension of the subraster 104 (denoted by X in FIG. 5) until thesubraster 104 is completed. The objective lens and mirror combinationreturns to its starting position and the receptor assembly 26incrementally translates the substrate in a direction along the widthdimension of the subraster 104 (denoted by Y in FIG. 5) to initiateengraving of a subsequent subraster. The translation increment is equalto the width dimension of the subraster 104. In a preferred embodiment,the width dimension of each subraster is about 33.3 mils and a total of300 subrasters are utilized to form the raster. Although the movement ofthe objective lens and mirror combination is described herein in variousphases or steps of the engraving process, it is understood that movementof these components is continuous throughout the engraving process.Table 1 below shows the data point content for both 1200 dpi and 2400dpi images in an 8′×10′ image format. TABLE 1 Operational Data PointContent for 8″ × 10″ Image Format Each Data Subraster Data Data TotalData Points Per Total Data Points Resolution Points Sets Subraster 300Subrasters 1200 dpi 40 9,600 384,000 115,200,000 2400 dpi 80 19,2001,536,000 460,800,000

[0032] During engraving, the laser 32 remains on. Instead of turning thelaser 32 on and off, the modulator 36 shifts the beam 30 to a positionanalogous to ON. An unshifted beam position is analogous to OFF. Duringengraving, this shift happens at a very high rate. In the OFF position,the beam 30 exits the modulator 36, strikes a dump mirror (not shown),and deflects into a beam dump (not shown) to absorb unwanted laserpower. When the modulator 36 shifts the beam 30 in an ON position, theshifted beam 30 bypasses the dump mirror and impinges on the scanner 20.Based on these ON and OFF positions, each data point or dot canrepresent an engraved point (ON) or an unengraved point (OFF) on thesurface of the substrate.

[0033]FIG. 6 depicts a functional block diagram of data handling of thesystem. As shown in FIG. 6, a master clock 200 operates at 480 kHz,which is the data rate for 2400 dpi resolution. The master clock 200 isstepped down to 120 kHz for 1200 dpi resolution. The data rate clocksclock an X-Y transport logic 210, which in turn drives an X-Y transportcontroller 212 for the transport assembly 24 (which moves the mirror 27and objective lens 28 in the X-direction) and the receptor assembly 26(which incrementally translates the substrate in the Y-direction). Thedata rate clocks also clock a modulation logic 310, which in turnoperates the modulator driver 38 that drives the modulator 36. Themaster clock 200 is stepped down further to provide a motor control, asshown in FIG. 6. The scanner 20 rotates at either 10,000 rpm (1200 dpi)or 20,000 rpm (2400 dpi). A motor controller 410 is clocked at 6 kHz for20,000 rpm and 3 kHz for 10,000 rpm to control a motor 412 that drivesthe scanner 20. An encoder signal is provided back to the motorcontroller from the scanner 20. S.O.S (Start of Scan) pulses from thescanner 20 and are fed to the modulation logic 310 and the X-Y transportlogic 210. Each S.O.S. pulse initiates the first data point of each dataset in the width dimension of the subrasters. Each S.O.S pulse alsotriggers the modulation sequence for each data set.

[0034] As already mentioned, a particular advantage of the system 10 isits ability to provide two different resolutions with the same opticalsystem (1200 dpi and 2400 dpi in a preferred embodiment). This isaccomplished by narrowing the modulation pulse width at 2400 dpi to halfof the modulation pulse width at 1200 dpi, while doubling its repetitionrate, which doubles the dot count along the subraster width from 40 to80. Correspondingly, the motor speed of the scanner is doubled from10,000 rpm to 20,000 rpm, which provides a full double-resolution dotarray (data set) across the width dimension of the subraster. Themodulation pulse width is narrowed by reducing the intensity of thebeam. Since the dots are formed by a Gaussian focused beam contour,reducing the pulse duration by one half reduces the dot exposure(intensity) on the substrate, which, in turn, sufficiently reduces thedot width to facilitate the double-resolution engraving. The repetitionrate of the modulation pulse width is changed via software control.Since the exposure (intensity) is reduced at the 2400 dpi resolution,the total energy remains the same as that at 1200 dpi resolution. Sincethe total energy is the same, the total engraving duration is the same.Thus, the system is capable of doubling its engraving resolution withoutincreasing engraving time.

[0035] From the foregoing description, it is apparent that changing theresolution of the system is rapidly accomplished without the need forcritical mechanical changes, such as changing the objective lens tofocus to a smaller dot size, which can be very costly. Furthermore, twodifferent resolutions can be engraved with the same optical system,which creates the same subraster format to cover the same total areaduring the same total time, and the same laser providing the sameoptical power.

[0036] As yet another aspect of the present invention, it has been foundthat the use of a thermoset plastic material as the substratesubstantially eliminates unwanted slag formation around the engravedpoints of the substrate. The thermoset plastic material substantiallyvaporizes in response to the impinging laser beam that engraves pointsof the substrate, thereby substantially eliminating the formation of theslag material. Desirable results have been achieved by including amineral filler with the thermoset material. Preferably, the mineralfiller has a grain size smaller than a smallest feature of the engravedportions of the substrate. Preferably, the grain size is in the range ofabout 3 to 5 microns. However, the grain size can be varied to match aparticular resolution. The filler adds strength to the substratematerial, thereby maintaining the accuracy and detail of the engravedportions of the substrate. In a preferred embodiment, silica is utilizedas a filler for the thermoset material. Additionally, a flame retardantcan be included to minimize flame and smoke formation from the impinginglaser beam.

[0037] Thermoset plastics provide for more accurate laser engraving due,in part, to their strength and resistance to flow. The polymer componentconsists of molecules with permanent cross-links between linear chainsthat form a rigid three-dimensional network structure which cannot flow.The tightly cross-linked structure of thermosetting polymers immobilizesthe molecules, providing hardness, strength at relatively hightemperature, insolubility, good heat and chemical resistance, andresistance to creep. The use of a thermoset plastic material for asubstrate has a significant impact on the cost of printing processesthat utilize such substrates. Thermoset plastic substrates are much lessexpensive than copper or steel substrates and they do not sacrificeengraving accuracy, and hence, printing accuracy.

[0038] It is contemplated that a variety of thermoset plastic materialscan be utilized in accordance with the principles of the presentinvention. Such materials include epoxies, unsaturated polyesters,phenolics, amino resins (such as urea- and melamine-formaldehyde),alkyds, allyl family (such as diallyphthalate), silicone moldingcompounds, and polyimides (such as bimaleimides).

[0039] In cases where durability is a priority, it has further beenfound that a substrate having an inorganic ceramic material is suitablefor a printing process, and particularly suitable for use in the systemand process described herein. In an embodiment as shown in FIG. 7, asubstrate 400 comprises a base material 402 and an inorganic ceramicmaterial 404 disposed on, and preferably bonded to, the base material402. Preferably, the base material 402 comprises a metal, such as, forexample, steel, aluminum, copper, iron or any other metal suitable foruse in a printing substrate. The ceramic material 404 provides a surfacefor formation of an image to be printed to a medium during a printingprocess. It is to be understood that other additional materials orlayers may be incorporated into the substrate 400, with the ceramicmaterial 404 providing the printing surface.

[0040] An inorganic ceramic material component, layer or coating of aprinting substrate provides excellent resistance to abrasion encounteredduring the printing process. Among other things, ink ingredients used inprinting processes can cause wear to the substrate. The ceramic materialof the substrate is more resistant to abrasion than the thermosetsubstrates, while offering excellent engraving accuracy. The substrateincorporating the inorganic ceramic material provides an excellentalternative to the thermoset substrates. It has been found that aninorganic ceramic material that is vitreous in nature offersparticularly excellent resistance to abrasion and is particularlysuitable for use in a printing substrate.

[0041] By way of background and example, a particular inorganic ceramicmaterial for use in a substrate for a printing process will now bedescribed with the understanding that the particular example is but oneembodiment of many as understood by one of ordinary skill in the artthat can be utilized in accordance with the principles of the presentinvention. In this particular example, the inorganic ceramic material isin the form of a porcelain enamel disposed on a metallic substrate, suchas a steel or iron substrate. Porcelain enamels for steel and ironsubstrates are typically classified as either ground-coat or cover-coatenamels. Ground-coat enamels contain metallic oxides, such as cobaltoxide and/or nickel oxide, that promote adherence of the glass/enamel tothe metal substrate. Cover-coat enamels are applied over fired groundcoats to improve the properties of the coating. In addition, cover-coatenamels may be applied over unfired ground coats, with both coats beingfired at the same time. This is referred to as a two-coat/one-firesystem. Cover coats may also be applied directly to properly prepareddecarburized steel substrates. Porcelain enamels for aluminum substratesare typically one-coat systems that are applied by spraying. However,two-coat systems can also be utilized. It should be understood, however,that any number of application systems, alone or in combination, can beutilized on various substrate materials to achieve a porcelain-coatedsubstrate.

[0042] The basic material of the porcelain enamel coating is calledfrit, which is a smelted complex borosilicate glass. Frits are producedby quenching a molten glassy mixture that is compounded from numerouscomponents, sometimes more than 20 different components, depending uponthe application. Thus, the composition of the frit can be customized andoptimized to exhibit certain desired properties for a particularapplication. As already mentioned, in cases where increased adherence toa steel substrate is desired, for example, cobalt oxide and/or nickeloxide may be included in the frit. In accordance with the principles ofthe present invention, the frit can be optimized for propertiesconducive to use as a printing substrate, including, but not limited to,hardness, abrasion resistance, strength at relatively high temperature,heat and chemical resistance, etc. Examples of oxide components that maybe utilized include, but are not limited to, SiO₂, B₂O₃, Na₂O, K₂O,Li₂O, CaO, ZnO, Al₂O₃, ZrO₂, TiO₂, CuO, MnO₂, NiO, Co₃O₄, P₂O₅, MgO,PbO, Sb₂O₃, Sb₂O₅, ZrO₂, BaO and F₂. Additives may be added to the fritto further influence various properties of the enamel, such as clay,bentonite, electrolytes, fluxes, and coloring oxides.

[0043] In a preferred embodiment, the porcelain enamel has a low glasscontent, i.e., less than 50% by weight, preferably in the range of35-40% by weight. However, other percentages can also be utilized, aslong as the glass content is not too low, which weakens the enamel.Typical porcelain enamels have a glass content between 50% and 60% byweight.

[0044] The porcelain enamel may be applied to the substrate by either awet process or a dry process. Wet process methods include manualspraying, electrostatic spraying, dipping, flow coating, andelectrodeposition (electrophoresis). Dry process methods includeelectrostatic dry powder spraying and sprinkling onto a heatedsubstrate. In a preferred embodiment, the porcelain enamel is appliedelectrostatically.

[0045] Since subsurface abrasion resistance varies with processingvariables that affect the bubble structure of the enamel (i.e., gasbubbles that get trapped in the enamel during cooling), it is preferablethat gas bubbles are minimized. Enamel compositions may containcrystalline particles (from mill additions or devitrification heattreatment) that can increase abrasion resistance by as much as 50%. In apreferred embodiment, calcium carbonate is included as a filleradditive, which increases abrasion resistance.

[0046] It should be understood that any inorganic ceramic material canbe utilized in accordance with the principles of the present invention.However, it is preferable to utilize a porcelain enamel, particularlyone having low glass content and exhibiting excellent abrasionresistance.

[0047] While some substrate materials—such as thermoset plastics—canaccommodate and take advantage of the faster engraving speeds and fasttrolley return speeds associated with the system 10 depicted in FIGS.1-6 (wherein only the objective lens and the mirror are carried on thetrolley assembly and moveable rapidly in the X direction while thesubstrate is stepped short distances moveable in the Y direction) othermaterials cannot be optimally engraved at higher speeds. In such cases,an alternate embodiment system 600 may be utilized as shown in FIG. 8,which is substantially identical to the system 10, with the primarydifference residing between the beam expander 22 and the receptorassembly 26, wherein the mirror 27 and the objective lens 28 (alsoreferred to as “mirror/objective lens combination”) remain in a fixedposition within the system 600. To simplify the descriptions herein,elements that are identical in system 10 and system 600 share the samereference indicia.

[0048] Referring to FIG. 8, the mirror/objective lens combination are ina fixed position and remain at a fixed distance with respect to the beamexpander 22 within the system 600. In this embodiment, the receptorassembly 26 supports the substrate to be engraved and is capable ofincrementally translating the substrate with respect to themirror/objective lens via a stepped transport in both the X and Ydirections. Thus, the engraving process is facilitated by translatingthe substrate in both directions while the mirror/objective lenscombination remains fixed to direct a fixed beam onto the substrate.This embodiment has been found to be effective with certain materialsdictating slower engraving speeds.

[0049] Software that facilitates the system to skip over non-engravedareas of the substrate at higher speeds can be incorporated intocontrols of both systems, the system having a moveable objective lensand the system having a fixed objective lens, to compensate for theslower engraving speeds dictated to these embodiments by the materialsthey are engraving.

[0050] It is understood that, given the above description of theembodiments of the invention, various modifications may be made by oneskilled in the art. Such modifications are intended to be encompassed bythe claims below.

What is claimed is:
 1. A substrate for use with a direct laser engravingprocess to create a printing substrate, the substrate comprising: a basematerial; and an inorganic ceramic material disposed on the basematerial.
 2. The substrate of claim 1, wherein the base materialcomprises a metal.
 3. The substrate of claim 1, wherein the inorganicceramic material is vitreous.
 4. The substrate of claim 1, wherein theinorganic material is bonded to the base material.
 5. The substrate ofclaim 1, wherein the base material is selected from the group consistingof steel, aluminum, copper and iron.
 6. The substrate of claim 1,wherein the inorganic ceramic material comprises a porcelain enamel. 7.The substrate of claim 6, wherein the porcelain enamel has a glasscontent less than 50 percent by weight.
 8. The substrate of claim 6,wherein the porcelain enamel has a glass content generally between 35 to40 percent by weight.
 9. The substrate of claim 6, wherein the porcelainenamel comprises an oxide selected from the group consisting of SiO₂,B₂O₃, Na₂O, K₂O, Li₂O, CaO, ZnO, Al₂O₃, ZrO₂, TiO₂, CuO, MnO₂, NiO,Co₃O₄, P₂O₅, MgO, PbO, Sb₂O₃, Sb₂O₅, ZrO₂, BaO and F₂.
 10. The substrateof claim 6, wherein the porcelain enamel includes a mineral filler. 11.The substrate of claim 10, wherein the mineral filler comprises calciumcarbonate.
 12. A printing substrate comprising: a base material; and aninorganic ceramic material disposed on the base material and having aformation defining an image to be printed on a medium during a printingprocess.
 13. The substrate of claim 12, wherein the base materialcomprises a metal.
 14. The substrate of claim 12, wherein the inorganicceramic material is vitreous.
 15. The substrate of claim 12, wherein theinorganic material is fused to the base material.
 16. The substrate ofclaim 12, wherein the formation defining the image is a laser-engravedformation.
 17. The substrate of claim 12, wherein the base material isselected from the group consisting of steel, aluminum, copper and iron.18. The substrate of claim 12, wherein the inorganic ceramic materialcomprises a porcelain enamel.
 19. The substrate of claim 18, wherein theporcelain enamel has a glass content less than 50 percent by weight. 20.The substrate of claim 18, wherein the porcelain enamel has a glasscontent generally between 35 to 40 percent by weight.
 21. The substrateof claim 18, wherein the porcelain enamel comprises an oxide selectedfrom the group consisting of SiO₂, B₂O₃, Na₂O, K₂O, Li₂O, CaO, ZnO,Al₂O₃, ZrO₂, TiO₂, CuO, MnO₂, NiO, Co₃O₄, P₂O₅, MgO, PbO, Sb₂O₃, Sb₂O₅,ZrO₂, BaO and F₂.
 22. The substrate of claim 18, wherein the porcelainenamel includes a mineral filler.
 23. The substrate of claim 22, whereinthe mineral filler comprises calcium carbonate.
 24. A substrate for usewith a direct laser engraving process to create a printing substrate,the substrate comprising: a metal layer; and a porcelain enamel layerbonded to the metal layer.
 25. The substrate of claim 24, wherein theporcelain enamel has a glass content less than 50 percent by weight. 26.The substrate of claim 24, wherein the porcelain enamel has a glasscontent generally between 35 to 40 percent by weight.
 27. The substrateof claim 24, wherein the porcelain enamel includes an oxide selectedfrom the group consisting of SiO₂, B₂O₃, Na₂O, K₂O, Li₂O, CaO, ZnO,Al₂O₃, ZrO₂, TiO₂, CuO, MnO₂, NiO, Co₃O₄, P₂O₅, MgO, PbO, Sb₂O₃, Sb₂O₅,ZrO₂, BaO and F₂.
 28. The substrate of claim 24, wherein the porcelainenamel includes a mineral filler.
 29. The substrate of claim 28, whereinthe mineral filler comprises calcium carbonate.
 30. A printing substratecomprising: a metal layer; and a porcelain enamel layer bonded to themetal layer and having a laser-engraved image to be printed on a mediumduring a printing process.
 31. The substrate of claim 30, wherein themetal layer is selected from the group consisting of steel, aluminum,copper and iron.
 32. The substrate of claim 30, wherein the porcelainenamel layer has a glass content less than 50 percent by weight.
 33. Thesubstrate of claim 30, wherein the porcelain enamel layer has a glasscontent generally between 35 to 40 percent by weight.
 34. The substrateof claim 30, wherein the porcelain enamel layer includes an oxideselected from the group consisting of SiO₂, B₂O₃, Na₂O, K₂O, Li₂O, CaO,ZnO, Al₂O₃, ZrO₂, TiO₂, CuO, MnO₂, NiO, Co₃O₄, P₂O₅, MgO, PbO, Sb₂O₃,Sb₂O₅, ZrO₂, BaO and F₂.
 35. The substrate of claim 30, wherein theporcelain enamel layer includes a mineral filler.
 36. The substrate ofclaim 35, wherein the mineral filler is calcium carbonate.
 37. Thesubstrate of claim 30, wherein the porcelain enamel layer has beenelectrostatically applied to the base layer.
 38. The substrate of claim30, wherein the porcelain enamel is formulated to be abrasive resistant.39. The substrate of claim 38, wherein the porcelain enamel isformulated to be abrasive resistant by a reduction of formation of gasbubbles within the enamel during application to the metal layer.
 40. Asubstrate for use in an intaglio printing process, the substratecomprising: a metallic base layer; and a porcelain enamel layer bondedto the base layer and having an engraved image created by laserengraving a plurality of subrasters each having a width and a length,each subraster defined by a plurality of data point sets each scannedacross the width of the subraster by a scanning beam incident to thesubstrate, each of the data point sets having data points that createone of either an engraved point or an unengraved point defined by astate of the scanning beam, the plurality of subrasters combining toform a raster defining the engraved image.
 41. A method of manufacturinga substrate for use with a direct laser engraving process to create aprinting substrate, the method comprising the steps of: providing ametallic layer; and disposing an inorganic ceramic layer on the metalliclayer.
 42. A method of making a printing substrate for use in a printingprocess, the method comprising the steps of: providing a substratecomprising a metallic layer and an inorganic ceramic layer disposed onthe metallic layer; and forming an image on the inorganic ceramic layerto be printed on a medium during a printing process.
 43. The method ofclaim 42, wherein the step of forming the image on the inorganic ceramiclayer comprises the step of engraving the image in the inorganic ceramiclayer.
 44. The method of claim 42, wherein the step of forming the imageon the inorganic ceramic layer comprises the step of laser engraving theimage in the inorganic ceramic layer.
 45. A method of making a printingsubstrate for use in a printing process, the method comprising the stepsof: providing a substrate comprising a metallic layer and an inorganicceramic layer disposed on the metallic layer; and engraving theinorganic ceramic layer with a plurality of subrasters each having awidth and a length, each subraster defined by a plurality of data pointsets each scanned across the width of the subraster by a scanning beamincident to the substrate, each of the data point sets having datapoints that create one of either an engraved point or an unengravedpoint defined by a state of the scanning beam, the plurality ofsubrasters combining to form a raster defining the engraved image.